diff --git a/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala b/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala
index e71460b806e3..486325b20cf2 100644
--- a/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala
+++ b/compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala
@@ -212,6 +212,8 @@ object GenericSignatures {
             else
               jsig(unboxedSeen, toplevel, primitiveOK)
           }
+          else if (defn.isXXLFunctionClass(sym))
+            jsig(defn.FunctionXXLType, toplevel, primitiveOK)
           else if (sym.isClass)
             classSig
           else
diff --git a/tests/generic-java-signatures/i3653.check b/tests/generic-java-signatures/i3653.check
new file mode 100644
index 000000000000..4824f908da06
--- /dev/null
+++ b/tests/generic-java-signatures/i3653.check
@@ -0,0 +1 @@
+public <T> scala.FunctionXXL Foo.bar()
diff --git a/tests/generic-java-signatures/i3653.scala b/tests/generic-java-signatures/i3653.scala
new file mode 100644
index 000000000000..4251aeb2f23b
--- /dev/null
+++ b/tests/generic-java-signatures/i3653.scala
@@ -0,0 +1,13 @@
+class Foo {
+  def bar[T] =
+    (a0: T, a1: T, a2: T, a3: T, a4: T, a5: T, a6: T, a7: T, a8: T, a9: T,
+     b0: T, b1: T, b2: T, b3: T, b4: T, b5: T, b6: T, b7: T, b8: T, b9: T,
+     c0: T, c1: T, c2: T, c3: T, c4: T, c5: T, c6: T, c7: T, c8: T, c9: T) => 0
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    val meth = classOf[Foo].getDeclaredMethod("bar")
+    println(meth.toGenericString)
+  }
+}